HP Support Assistant is the oft-default tool, not suitable for automation; but there is the HP Image Assistant:
ftp.ext.hp.com/pub/caps-softpaq/cmit/HPIA.html
So far this looks like the way forward. Early testing done, not thorough yet. It has a GUI for default use, but also has command line usage. Download the installer, complete it, CD to the folder it created in command-line, and run HPImageAssistant.exe for nice GUI. Documentation is here:
ftp.hp.com/pub/caps-softpaq/cmit/imagepal/userguide/936944-008.pdf
Several command-line examples are in that PDF. This command does a lot of very good things, very silently:
.\HPImageAssistant /Operation:Analyze /Category:All,Accessories /selection:All /action:Install /silent /reportFolder:c:\HPIA\Report /softpaqdownloadfolder:c:\HPIA\download